The present invention relates to a method of manufacturing a semiconductor device with a multi-layer interconnection structure.
FIG. 3 shows a conventional method of manufacturing a semiconductor device with multi-layer interconnection structure described in JP, 7-240466, A. In this method, first, as shown in FIG. 3A, a lower wiring layer 12 is formed on a semiconductor substrate 11. Following this, an inter-layer insulation layer 13 of SiO2 or the like and a stopper film 14 of SiN are successively stacked. The inter-layer insulation layer 13 and the stopper film 14 are thereafter etched using a resist mask (not shown), thereby forming an aperture portion 15. A plug layer 16 of tungsten or the like is formed so as to fill up the aperture portion 15.
Following this, as shown in FIG. 3B, the plug layer 16 is etched back using the stopper film 14 as an etching stopper. The plug layer 16 is over-etched so as to completely remove the plug layer 16 on the stopper film 14. Therefore, the top surface of the plug layer 16 becomes slightly lower than the surface of the stopper film.
Next, as shown in FIG. 3C, the stopper film 14 is removed using phosphoric acid. In consequence, the top surface of the plug layer 16 projects above the surface of the inter-layer insulation layer 13.
At last, as shown in FIG. 3D, an upper wiring layer 17 is formed. The steps described above complete a semiconductor device with a multi-layer interconnection structure 200 in which the plug layer 16 connects the lower wiring layer 12 with the upper wiring layer 17.
During these steps, since the top surface of the plug layer 16 projects above the surface of the inter-layer insulation layer 13 as shown in FIG. 3C, the connection between the plug layer 16 and the upper wiring layer 17 becomes perfect.
However, as an aperture size of the aperture portions 15 becomes small in semiconductor devices because of increasing progress of integration, the size and shape of the aperture portions 15 become various. Consequently the connection, etc., between the plug layer 16 and the upper wiring layer 17 becomes imperfect.
Research on a cause of this identified that during exposure of a resist layer (not shown) formed on the stopper film 14, exposure light reflected by the surfaces of the stopper film 14 and the inter-layer insulation layer 13 once again impinges upon and sensitizes the resist layer, and therefore, it is impossible to precisely form a fine resist pattern. The reflection of the exposure light, in particular, was found to be remarkable in the case of exposure light with a short wavelength such as an excimer laser.
Noting this, the present invention aims at providing a method to manufacture a multi-layer interconnection structure which uses a stopper film, with which it is possible to precisely form a fine resist pattern on the stopper film.
The present invention is directed to a manufacturing method for a semiconductor device with a multi-layer interconnection structure, comprising: a step to prepare a semiconductor substrate; a step to form an inter-layer insulation layer on said semiconductor substrate; a silicon nitride film forming step to form a silicon nitride film on said inter-layer insulation layer; a step to form a photoresist layer on said silicon nitride film and exposing said photoresist with an excimer laser to thereby form a resist mask; an etching step to etch at least said silicon nitride film using said resist mask as an etching mask to thereby form an aperture portion; a step to deposit a conductive layer within said aperture portion and on said silicon nitride film; a step to etch back said conductive layer on said silicon nitride film using said silicon nitride film as a stopper so that the conductive layer remaining within said aperture portion becomes a plug layer; a step to remove the silicon nitride film so that a top end of the plug layer protrudes above the surface of the inter-layer insulation layer; and a step to form a wiring layer connected with said plug layer on said inter-layer insulation layer, wherein said silicon nitride film forming step is a step to select the film thickness of said silicon nitride film in such a manner that reflection light of said excimer laser which impinges upon said photoresist layer from the back surface of the photoresist layer decreases.
With the reflection light decreased in this manner, it is possible to accurately and precisely form a resist mask with a fine opening pattern. As a result, it is possible to form highly-integrated multi-layer interconnection structures with an excellent reproducibility and at a high yield.
The silicon nitride film forming step described above is preferably a step to select the film thickness of said silicon nitride film in such a manner that a reflectance ratio of the reflection light of the excimer laser relative to incident light is 0.3 or lower.
Since the reflectance ratio is 0.3 or lower, it is possible to precisely form a finer resist pattern.
The silicon nitride film forming step described above is preferably a step to select the film thickness of said silicon nitride film from the range of about 1200 xc3x85 to about 1340 xc3x85 and the range of about 1730 xc3x85 to about 1880 xc3x85.
As the silicon nitride film has such a film thickness, it is possible to ensure that the reflectance ratio of the excimer laser is 0.3 or smaller.
The silicon nitride film forming step described above is preferably a step to select the film thickness of the silicon nitride film from the range of about 1230 xc3x85 to about 1310 xc3x85 and the range of about 1760 xc3x85 to about 1850 xc3x85.
As the silicon nitride film has such a thickness, it is possible to ensure that the reflectance ratio of the excimer laser is 0.2 or lower.
The silicon nitride film forming step is preferably a step to select either about 1270 xc3x85 or about 1800 xc3x85 for the film thickness of said silicon nitride film.
As the silicon nitride film has such a film thickness, it is possible to minimize the reflectance ratio of the excimer laser.
A wavelength of the excimer layer described above is about 248 nm. The thickness of the silicon nitride film described above is effective in reducing the reflectance ratio of the excimer laser with this wavelength.
The etching step described above preferably comprises a step to etch the silicon nitride film using the resist mask described above, and after removing said resist mask, further to etch the inter-layer insulation layer mentioned above using said silicon nitride film as a mask.
Etching the inter-layer insulation layer using the silicon nitride film as a mask, it is possible to prevent the mask from receding during the etching, and hence, to precisely form an aperture portion with a high aspect ratio.
A step may be exercised which requires to form other wiring layer on the semiconductor substrate so that the plug layer mentioned above is connected to said other wiring layer.
As clearly described above, using the manufacturing method according to the present invention, it is possible to form a fine resist pattern at a step which uses a stopper film of silicon nitride. As a result, it is possible to precisely form a highly-integrated multi-layer interconnection structure.